Emily White, 19, said she was on a night out in Newquay when a doorman at the Sailors Arms leered at her and made comments about her breasts. When she threatened to report him, Ms White said, she was told: "They won't do anything love."
The pub said it took "immediate action" after receiving the complaint and an investigation was under way.
Ms White, from St Austell, Cornwall, said the harassment started with a wolf-whistle but soon became more intimidating, with the doorman leering at her and making comments about her breasts.
In a tweet which has been shared more than 8,000 times and liked by more than 90,000 users, she wrote: "He told me: 'I'm a bouncer I can do what I want'."
"No mate, no you can't," she added.
Was sexually harassed by a bouncer in a night club this weekend. So I snapped a photo of his ID, emailed the club, who have emailed his agency, who have begun an official displinary investigation. He told me, “I’m a bouncer I can do what I want”. No mate, no you can’t.
— em (@itsemilywhite) July 24, 2018
In response to her threatening to complain, Ms White said the bouncer "moved his arm out so I could take a picture of his ID".
"That's how cocky he was."
"He thought no-one would challenge him on it," she said. "He was wrong."
Ms White said she had been overwhelmed by the number of people who responded to her post.
"It's not the worst thing that's happened to a girl. It's not even the worst thing that's happened to me," she said.
"But I was able to report it and so I did. If the same thing has happened to anyone else, I would urge them to do the same."
A spokesperson for the Sailors Arms said: "Upon hearing of these allegations, an immediate investigation was launched in collaboration with the agency which employs our door staff. Until it is complete, the individual in question will not be employed at our door."
Regency Security, the firm that supplies door staff to the venue, declined to comment.
Sexual harassment is defined as "any unwanted behaviour of a sexual nature that you find offensive or which makes you feel distressed, intimidated or humiliated".
Types of sexual harassment can include:
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